The prior application relates to carboxymethyl esters of mercaptopropanoic acids which have the formula ##STR2## wherein R is hydrogen or lower alkanoyl; R.sub.1 is hydrogen or lower alkyl; R.sub.2 is hydrogen, lower alkyl, phenyl, phenyl-lower alkyl, 4-hydroxyphenyl-lower alkyl or indolyl-lower alkyl; and salts thereof.
In the parent application those compounds of the above formula wherein R.sub.2 is indolyl-lower alkyl have been held to constitute a different invention. Upon additional experimentation, it has been found that a group of compounds of the above type, characterized by the presence of an indolyl-lower alkyl group, constitute a particularly interesting group as described below.